"It is the toughest film I am doing. Shankar (director) is not happy with anything I am doing. I am trying to create something unique for India and the world," Rahman said.
The composer had collaborated with S Shankar for the 2010 science fiction drama "Enthiran" ('Robot' in Hindi) with Rajinikanth, Aishwarya Rai Bachchan and Danny Denzongpa in the lead roles.
Even the southern superstar feels it is a tough job to please Shankar.
"To work with Shankar is difficult. He is a perfectionist.
That is why he is one of the biggest directors. This picture as 3D is a different experience," the 65-year-old actor said.
Amy Jackson, who is working with Rajinikanth for the first time was euphoric for being a part of the project.
"I had no idea that I would be a part of this film with these legends. I was intimidated initially but on sets, everyone was like my family," she said.